docs: def total_memory(self, image='ubuntu'):
          '''Get the available ram fo the docker machine in Kb'''
          try:
              ret = subprocess.check_output(
                  f'''docker run -t {image} cat /proc/meminfo  | grep MemTotal''',
                  shell=True,
                  stdin=subprocess.DEVNULL)
              # ret: MemTotal:       30208916 kB
              self.tot_mem = int(ret.split()[1])
          except Exception:
              # some system does not have cat or grep
              self.tot_mem = None
          return self.tot_mem